NEW YORK (Reuters Health) - Measles antibodies are apparent for at least 10 years after receipt of a second dose of the measles vaccine, according to findings from a study conducted in the US, a country declared free of measles in 2000.

Previous reports have suggested that the immunity induced by the measles vaccine lasts many years and possibly forever. However, most of the supporting studies were performed at a time when wild-type measles was still present and, thus, boosting of the immune response was likely to occur.

The goal of the present study, therefore, was to examine the persistence of vaccine-induced immunity in a post-elimination environment, lead author Dr. Charles W. LeBaron, from the Centers for Disease Control and Prevention in Atlanta, and colleagues note.

The study, reported in the Archives of Pediatric and Adolescent Medicine for March, involved 621 children enrolled in a Wisconsin health maintenance organization who received a second measles vaccine dose in 1994 or 1995, while in kindergarten or middle school.

Serum samples were collected periodically over 5- and 10-year periods for the middle school and kindergarten groups, respectively. The final study group, 364 subjects, was the result of voluntary attrition and this group did not differ significantly in characteristics from the original group.

No cases of measles were reported in the study area during the study period.

One month after the second vaccine dose, 0.2% of subjects had low measles antibody titers, but none were seronegative, the report indicates.At 1 month follow-up, kindergartners had significantly higher geometric mean titers than did middle schoolers. However, by the time subjects in each group reached 15 years of age, no significant difference in geometric mean titers was seen. The percentage of subjects with low antibody titers rose to 4.9%, but still none of the subjects were seronegative.

"We believe our study demonstrates that the US routine 2-dose measles vaccination strategy can produce high rates of seropositivity that persist for as long as 10 years after the second dose, even in the absence of wild-type virus boosting," the researchers conclude.